Electrode active materials for lithium secondary batteries, method for preparing the same, and lithium secondary batteries using the same

ABSTRACT

An electrode active material further comprising an amphoteric compound, an alkali metal sulfide or an alkali metal oxide, and lithium secondary batteries using the electrode active material, are disclosed. The lithium secondary batteries neutralize acids generating around electrode active material so that it can inhibit the reduction in battery capacity. In addition, the lithium secondary batteries are excellent in its charge-discharge characteristics, cycle life and thermal stability. A method for preparing the electrode active material for lithium secondary batteries is also provided.

TECHNICAL FIELD

The present invention relates to an electrode active material forlithium secondary batteries, a method for preparing the same and lithiumsecondary batteries using the same, and more particularly to a positiveelectrode or a negative electrode active material for lithium secondarybatteries which further comprises an amphoteric compound, an alkalimetal sulfide or an alkali metal oxide, a method for preparing theelectrode active material and lithium secondary batteries using theelectrode active material.

BACKGROUND ART

Secondary batteries are used as a power supplier of portable electronicdevices for information communications such as PDA, cellular phones,notebook computers, etc., electric bicycles, electric automobiles, andthe like. Therefore, there is a growing demand for the secondarybatteries capable of repeatedly charging and discharging. In particular,since the performance of the devices depends on secondary batteries,high performance secondary batteries are required. The characteristicsrequired for secondary batteries include charge-dischargecharacteristics, life characteristics, high-rate characteristics,thermal stability at high temperature and the like. In addition, lithiumsecondary battery has been drawn attention in terms of high voltage andenergy density.

Lithium secondary batteries are classified into lithium batteries usinglithium metal as a negative electrode and lithium ion batteries usingcarbon capable of intercalating/deintercalating lithium ion as aninterlayer compound. Further, lithium secondary batteries are oftenclassified into liquid type batteries, gel type polymer and solid typepolymer batteries according to the used electrolytes.

Lithium secondary batteries are commonly comprised of a positiveelectrode, a negative electrode, an electrolyte, a separator, apackaging material, etc. The positive electrode is prepared bydispersing a mixture of a lithium transition metal composite oxide suchas LiCoO₂, LiMn₂O₄, LiNiO₂, or LiMnO₂ as a positive electrode activematerial, an electrically conductive agent and a binder into a currentcollector. The active materials have a high electrochemical potentialduring intercalation/deintercalation reaction by lithium ion. The activematerial for a negative electrode includes lithium, carbon, or the like,which has a low electrochemical potential.

The electrolyte is prepared by dissolving a lithium ion-containing saltsuch as LiPF₆, LiBF₄, LiClO₄, etc., in a polar organic solvent such asethylene carbonate, propylene carbonate, dimethyl carbonate, diethylcarbonate, methylethyl carbonate, etc. The separator mainly usespolyolefin-based polymer such as porous polyethylene for ion conductinglayer and electrical insulation between anode and cathode. The packagingmaterial which protects the contents of battery and provides a path ofelectrical signal includes a metal can made of iron or aluminum, or amultilayer of aluminum foil and polymer film.

However, lithium secondary batteries have many problems, e.g., the lifeof battery may be shortened by a repeated charge/discharge cycle,particularly at high temperature. This is because electrolyte isdecomposed, active material is deteriorated, or internal resistance ofbattery increases, due to moisture present in the battery, etc.

Many efforts to solve these problems have been made. For example, KoreanPatent Publication No. 10-277796 discloses a method for coating metaloxides such as Mg, Al, Co, K, Na, Ca, etc., onto the surface of positiveelectrode active material by heat treatment. A technique for increasingenergy density and high-rate characteristics by adding TiO₂ to LiCoO₂ asan active material is disclosed in the “Electrochemical and Solid-StateLetters, 4(6), A65-A67 (2001). A technique for improving battery life bysurface-treating natural graphite with aluminum is disclosed in theElectrochemical and Solid-State Letters, 4(8), A109-A112 (2001).However, there still exist problems such as life deterioration and thegeneration of gas due to electrolyte decomposition during charging anddischarging cycle.

In addition, a problem that electrolyte is oxidized due to the reductionin battery capacity during charging, and the resulting acid dissolvesactive material is disclosed in the Journal of Electrochemical Society,143(1996), p2204.

DISCLOSURE OF THE INVENTION

The present inventors have earnestly and intensively researched tosearch causes of deterioration in battery performance during a repeatedcharge and discharge cycle. As a result, they have found that whenmaterial capable of neutralizing acids generating around electrodeactive material is added, the deterioration in battery performance canbe inhibited. In particular, they have found that when amphotericcompound, alkali metal sulfide or alkali metal oxide is added toelectrode active material, charge-discharge characteristics, lifecharacteristics and high-rate characteristics of the batteries can beimprove, and the generation of gas inside the battery can be inhibited.

Therefore, it is an object of the present invention is to provide anelectrode active material for lithium electrode active material forlithium secondary batteries which can improve charge-dischargecharacteristics, life characteristics and high-rate characteristics ofthe batteries and inhibit the generation of gas inside the battery.

It is another object of the present invention is to provide a method forpreparing the electrode active material for lithium electrode activematerial for lithium secondary batteries.

It is yet another of the present invention is to provide lithiumsecondary batteries using the electrode active material for lithiumsecondary batteries.

In accordance with the present invention, the above and other objectscan be accomplished by the provision of an electrode active material forlithium secondary batteries further comprising an amphoteric compound,an alkali metal sulfide or an alkali metal oxide.

The electrode may be a positive electrode or a negative electrode. As apositive electrode active material, any active material in the form ofpowder having an oxidation/reduction potential of from 1.5V to 6.0V,based on the oxidation/reduction potential of lithium metal may be usedin the present invention. Preferably, the active material includeslithium transition metal composite oxides, lithium transition metalcomposite chalcogen compounds and a mixture thereof containing variouselements, but is not limited to these compounds. More preferably, thepositive electrode active material includes compounds represented by thefollowing formula (1):Li_(a)M_(b)N_(c)L_(d)O_(e)P_(f)Q_(g)  (1)

-   -   wherein,    -   a, b, c and d are independently an equivalent number from 0 to        2,    -   L, M and N are independently selected from the group consisting        of Mn, Co, Ni, Fe, Cu, Cr, Sr, Ti, V, Cu, Zn and Al,    -   e, f and g are independently an equivalent number from 0 to 4,        and    -   O, P and Q are independently selected from the group consisting        of O, S and F.

As a negative electrode active material, any active material in the formof powder having an oxidation/reduction potential of from 0.001V to3.5V, based on the oxidation/reduction potential of lithium metal may beused in the present invention. Preferably, the negative electrode activematerial includes graphite consisting of carbon and compoundsrepresented by the following formulae (2) to (4):A_(x)B_(y)M_(a)N_(b)  (2)

-   -   wherein    -   x, y, a and b are independently an equivalent number from 0 to        4,    -   A and B are independently selected from the group consisting of        Mn, Co, Ni, Fe, Cu, Cr, Sr, Ti, V, Cu and Zn, and    -   M and N are independently selected from the group consisting of        O, S, F, Cl, Br, I, Se, Te and Fr.        Si_(x)M_(y)  (3)    -   wherein    -   x and y are independently an equivalent number from 0 to 2, and    -   M is one element selected from the group consisting of Mn, Co,        Ni, Fe, Cu, Cr, Sr, Ti, V, Cu, Zn, Al and B.        SnO_(x)M_(y)  (4)    -   wherein    -   x and y are independently an equivalent number from 0 to 4, and    -   M is one element selected from the group consisting of O, S, F,        Cl, Br, I, Se, Te and Fr.

The term ‘amphoteric compound’ referred to herein includes all compoundscontaining at least one amphoteric element. The amphoteric compound iscapable of neutralizing acids generating around the electrode activematerial. Examples of amphoteric elements include zinc, tin, lead,boron, antimony, arsenium, etc. The compound containing the amphotericelement includes zinc acetate, zinc acetylacetonate, zinc bromide, zinccarbonate, zinc chloride, zinc iodide, zinc nitrate and zinc oxide.Examples of tin-containing compounds include tin acetate(II), tinacetate(IV), tin oxalate(II), tin oxide(II) and tin chloride(II).Examples of lead-containing compounds include lead acetate(II), leadacetate(IV), lead carbonate(II), lead chloride(II), lead nitrate(II) andlead oxide(II). Examples of boron-containing compounds include boronoxide, boron phosphate, boron bromide, boron chloride, and borontrifluoride diethyl etherate (C₂H₅)₂OBF₃). Examples ofantimony-containing compounds include antimony oxide(III), antimonytrichloride(III) and antimony pentachloride(V). Examples ofarsenium-containing compounds include arsenium oxide(III), arseniumtrichloride(III) and arsenium pentachloride(V). In addition to thesecompounds, any compound that can react with acids may be used, so longas they do not damage to battery characteristics.

Examples of the alkali metal sulfide include Li₂S, Na₂S, K₂S, Rb₂S,Cs₂S, etc., and examples of the alkali metal oxide include Li₂O, Na₂O,K₂O, Rb₂O, Cs₂O, etc.

The present invention also relates to a method for preparing theelectrode active material for lithium secondary batteries. The methodcomprises the steps of: adding a positive electrode or a negativeelectrode active material to a solution of compound selected from thegroup consisting of amphoteric compounds, alkali metal oxides and alkalimetal sulfides in an appropriate solvent; homogeneously dispersing themixture; and filtrating and drying the dispersed mixture to remove thesolvent. The electrode active material thus prepared has a particle sizeof from 1 μm to 40 μm, and preferably from 5 μm to 25 μm. If necessary,the solvent-removed powder may be heat-treated at a temperature of from10° C. to 500° C. for 1˜10 hours to coat onto the electrode activematerial.

Specifically, first, 0.1˜20% by weight of the compound selected from thegroup consisting of amphoteric compounds, alkali metal oxides and alkalimetal sulfides is dissolved in a solvent such as alcohol, e.g.,methanol, ethanol and isopropanol, or water. Subsequently, the positiveelectrode active material or negative electrode active material is addedto the solution, and the mixture is homogeneously dispersed using anultrasonic transducer. Finally, the dispersed mixture is filtered anddried in a conventional process to prepare the electrode active materialfor lithium secondary batteries. Herein, the amount of the compoundselected from the group consisting of amphoteric compounds, alkali metalsulfides and alkali metal oxides is within the range of from 0.01% to 5%by weight, and preferably from 0.1% to 2% by weight, based on the weightof the electrode active material. When the amount is smaller than 0.01%by weight, the neutralizing effect on the resulting acids is weak. Whenthe amount exceeds 5% by weight, the energy density of battery isreduced.

The present invention also relates to lithium secondary batteries usingthe electrode active material for lithium secondary batteries. Thelithium secondary batteries can be manufactured by homogeneouslyapplying a mixture of the electrode active material, a binder and anelectrically conductive agent onto an aluminum foil or copper foil, anddrying to prepare a electrode, and fabricating using an separator, anelectrolyte, a packaging material, etc.

The electrolyte usable in the present invention may be a solution of atleast one lithium salt selected from the group consisting of LiCF₃SO₃,Li(CF₃SO₂)₂, LiPF₆, LiBF₄, LiClO₄ and LiN(SO₂C₂F₅)₂ in a solventselected from the group consisting of ethylene carbonate, propylenecarbonate, dimethyl carbonate, diethyl carbonate, methylethyl carbonate,vinylidene carbonate, γ-butyrolactone, etc., or a mixed solvent thereof.The separator usable in the present invention may be polyolefin-basedpolymer such as porous polyethylene. The packaging material usable inthe present invention may be a metal can or a multilayered of aluminumfoil and polymer film.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a graph comparing the cycle life of the battery manufacturedin Example 1 at high temperature with that of the battery manufacturedin Comparative Example 1:

FIG. 2 is a graph comparing the cycle life of the battery manufacturedin Example 2 at high temperature with that of the battery manufacturedin Comparative Example 2:

FIG. 3 is a graph comparing the cycle life of the battery manufacturedin Example 3 with that of the battery manufactured in ComparativeExample 3:

FIG. 4 is a graph comparing the cycle life of the battery manufacturedin Example 4 with that of the battery manufactured in ComparativeExample 4: and

FIG. 5 is a graph comparing the cycle life of the battery manufacturedin Example 10 with that of the battery manufactured in ComparativeExample 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereafter, the present invention will be more specifically explainedwith reference to examples shown below. However, the present inventionis not limited by these examples.

EXAMPLE Example 1

i) Preparation of Positive Electrode Active Material

0.1 g of zinc acetate (Aldrich) was dissolved in 5 g of distilled water,and 10 g of LiMn₂O₄ powder (Carus Corp., HU-1) was added thereto. Afterthe mixture was mixed homogeneously, the mixture was subjected tosonication for 1 hour. Subsequently, the mixture was dried in athermostatic oven of 120° C. for 10 hours to prepare a positiveelectrode active material.

ii) Manufacture of Positive Electrode

0.5 g of carbon black and 0.5 g of polyvinylidene fluoride were added tothe positive electrode active material prepared in i), and mixedhomogeneously. To the mixture, 5 g of N-methylpyrrolidone (NMP) wasadded. The resulting mixture was applied onto an aluminum foil having athickness of 20 μm, dried at a temperature of 100° C. to manufacture apositive electrode.

iii) Manufacture of Coin Battery

The positive electrode manufactured in ii), lithium foil as a counterelectrode, porous polyethylene membrane (Celgard LLC, Celgard 2300,thickness: 25 μml) as a separator, and a solution of 1M LiPF₆ in a mixedsolvent of ethylene carbonate and dimethyl carbonate (1:1(v/v)) as anelectrolyte were used to manufacture a coin battery, in accordance witha conventional manufacturing process. The battery characteristics of thecoin battery thus manufactured were tested under a voltage between 4.35Vand 3.30V with 1 CmA at a temperature of 55° C. by an electrochemicalanalysis apparatus (One A Tech, Automatic Battery Cycler, WBCS3000).

Example 2

0.1 g of zinc acetate was dissolved in 5 g of distilled water, and 2.5 gof LiNi_(0.5)Mn_(1.5)O₄ powder was added thereto. After the mixture wasmixed homogeneously, the mixture was subjected to sonication for 1 hour.Subsequently, the mixture was dried in a in a thermostatic oven of 120°C. for 10 hours to remove water. The dried mixture was heat-treated andcoated with ZnO to prepare a positive electrode active material.

A positive electrode and a coin battery were manufactured in the samemanner as ii) and iii) of Example 1.

Example 3

0.1 g of zinc acetate was dissolved in 5 g of methanol, and 2.5 g ofLiMnO₂ powder, which was synthesized at low temperature, was addedthereto. After the mixture was mixed homogeneously, the mixture wassubjected to sonication for 1 hour. Subsequently, the mixture was driedin a thermostatic oven of 120° C. for 10 hours to prepare a positiveelectrode active material.

A positive electrode and a coin battery were manufactured in the samemanner as ii) and iii) of Example 1.

Example 4

0.1 g of zinc acetate was dissolved in 5 g of distilled water, and 2 gof Li_(1.1)MnO₂ powder was added thereto. After the mixture was mixedhomogeneously, the mixture was subjected to sonication for 1 hour.Subsequently, the mixture was dried in a thermostatic oven of 120° C.for 10 hours to prepare a positive electrode active material.

A positive electrode and a coin battery were manufactured in the samemanner as ii) and iii) of Example 1.

Example 5

A positive electrode and a coin battery were manufactured in the samemanner as Example 1, except that tin acetate(II) was used instead ofzinc acetate.

Example 6

A positive electrode and a coin battery were manufactured in the samemanner as Example 1, except that lead acetate(II) was used instead ofzinc acetate.

Example 7

A positive electrode and a coin battery were manufactured in the samemanner as Example 1, except that boron phosphate was used instead ofzinc acetate.

Example 8

A positive electrode and a coin battery were manufactured in the samemanner as Example 1, except that antimony acetate(II) was used insteadof zinc acetate.

Example 9

i) Preparation of Negative Electrode Active Material

0.1 g of zinc acetate was dissolved in 5 g of water, and 10 g ofgraphite powder was added thereto. After the mixture was mixedhomogeneously, the mixture was subjected to sonication for 1 hour.Subsequently, the mixture was dried in a thermostatic oven of 200° C.for 10 hours to prepare a negative electrode active material.

ii) Manufacture of Negative Electrode

1 g of polyvinylidene fluoride was added to the negative electrodeactive material prepared in i), and mixed homogeneously. To the mixture,10 g of N-methylpyrrolidone (NMP) was added. The resulting mixture wascoated onto an copper foil having a thickness of 12 μm, dried at atemperature of 100° C. to manufacture a negative electrode.

iii) Manufacture of Coin Battery

The negative electrode manufactured in ii), lithium foil as a counterelectrode, porous polyethylene membrane (Celgard LLC, Celgard 2300,thickness: 25 μm) as a separator, and a solution of 1M LiPF₆ in a mixedsolvent of ethylene carbonate and dimethyl carbonate (1:1 (v/v)) as anelectrolyte were used to manufacture a coin battery, in accordance witha conventional manufacturing process.

The battery characteristics of the coin battery thus manufactured weretested under a voltage between 2.0V and 0.10V with 1 CmA at roomtemperature by an electrochemical analysis apparatus (One A Tech,Automatic Battery Cycler, WBCS3000).

Example 10

10 g of graphite and 0.1 g of Sn₂P₂O₇ powder were dissolved in 10 g ofisopropyl alcohol. After the mixture was mixed homogeneously, themixture was subjected to heat treatment at a temperature of 200° C.

A negative electrode and a coin battery were manufactured in the samemanner as ii) and iii) of Example 9.

Example 11

A negative electrode and a coin battery were manufactured in the samemanner as ii) and iii) of Example 9, except that tin acetate(II) wasused instead of zinc acetate.

Example 12

A negative electrode and a coin battery were manufactured in the samemanner as ii) and iii) of Example 9, except that lead acetate was usedinstead of zinc acetate.

Example 13

A negative electrode and a coin battery were manufactured in the samemanner as ii) and iii) of Example 9, except that boron phosphate wasused instead of zinc acetate.

Example 14 Manufacture of Lithium Secondary Battery

The positive electrode manufactured in ii) of Example 1, the negativeelectrode manufactured in ii) of Example 9, porous polyethylene membrane(Celgard LLC, Celgard 2300, thickness: 25 μm) as a separator, and asolution of 1M LiPF₆ in a mixed solvent of ethylene carbonate anddimethyl carbonate (1:1 (v/v)) as an electrolyte were used tomanufacture a lithium secondary battery, in accordance with aconventional process for manufacturing lithium secondary battery.

Example 15

Graphite powder was treated with zinc acetate solution in Example 9 andheat-treated at a temperature of from 200° C. to 2000° C. Subsequently,a coin battery was manufactured in the same manner as Example 9.

Examples 16˜25

Positive electrode active materials, positive electrodes and coinbatteries were manufactured in the same manner as Example 1, except thatLi₂S, Na₂S, K₂S, Rb₂S, CS₂S, Li₂O, Na₂O, K₂O, Rb₂O and Cs═O,respectively, were used instead of zinc acetate.

Examples 26˜35

Negative electrode active materials, negative electrodes and coinbatteries were manufactured in the same manner as Example 9, except thatLi₂S, Na₂S, K₂S, Rb₂S, Cs₂S, Li₂O, Na₂O, K₂O, Rb₂O and Cs₂O,respectively, were used instead of zinc acetate.

Example 36

0.1 g of zinc acetate (Aldrich) was dissolved in 5 g of distilled water,and 10 g of LiMn2O4 powder (Carus Corp., HU-1) was added thereto. Afterthe mixture was mixed homogeneously, the mixture was subjected to ballmilling for 20 hour. Subsequently, the mixture was dried in athermostatic oven of 50° C. for 1 hour. The resultant powder wascalcined at 450° C. for 5 hr in air atomosphere.

Comparative Example Comparative Example 1

A coin battery was manufactured in the same manner as ii) and iii) ofExample 1, except that LiMn₂O₄ powder was not treated with zinc acetate.

Comparative Example 2

A coin battery was manufactured in the same manner as ii) and iii) ofExample 1, except that LiN_(0.5)Mn_(1.5)O₄ powder was used as a positiveelectrode active material.

Comparative Example 3

A coin battery was manufactured in the same manner as ii) and iii) ofExample 1, except that LiMnO₂ powder was used as a positive electrodeactive material.

Comparative Example 4

A coin battery was manufactured in the same manner as ii) and iii) ofExample 1, except that LiMn_(1.1)O₂ powder was used as a positiveelectrode active material.

Comparative Example 5

A coin battery was manufactured in the same manner as ii) and iii) ofExample 9, except that graphite was used as a negative electrode activematerial.

Experimental Example 1 Cycle Life of Battery

The cycle life of the batteries of Example 1 and Comparative Example 1under a voltage between 4.35V and 3.30V with 1C at a temperature of 55°C. was shown in FIG. 1. As shown in FIG. 1, in case of the battery ofExample 1, 98% of the initial capacity was maintained even if the numberof cycle was above 25; whereas in case of the battery of ComparativeExample 1, only about 82% of the initial capacity was maintained at thenumber of cycle of above 25.

The cycle life of the batteries of Example 2 and Comparative Example 2under a voltage between 5.3V and 3.5V with 0.3C at a temperature of 55°C. was shown in FIG. 2. As shown in FIG. 2, the initial capacity of thebattery of Comparative Example 2 was 133 mAh/g, but was sharply reducedalong with the number of cycle to be 27% (36 mAh/g) of the initialcapacity after 50 cycles. On the other hand, the initial capacity of thebattery of Example 2 was 137 mAh/g, and was maintained to 136 mAh/g evenif the number of cycle was above 50. That is, the reduction in batterycapacity did not appeared.

This suggests that in case of the electrode not coated with zinc acetate(Comparative Example 2), Mn included in the positive electrode materialwas dissolved by hydrofluoric acid and, as a result, the initialcapacity was sharply reduced. However, in case of the electrode coatedwith zinc acetate (Example 2), zinc acetate present on the surface ofthe positive electrode material was reacted with hydrofluoric acid toform ZnF₂, thereby inhibiting the elution of Mn.

The cycle life of the batteries of Example 3 and Comparative Example 3when charge-discharged at room temperature was shown in FIG. 3. As shownin FIG. 3, the initial capacity of Comparative Example 3 was 186 mAh/g,but was sharply reduced along with the number of cycle to be 166 mAh/gafter 69 cycles. On the other hand, the initial capacity of the batteryof Example 3 was 185 mAb/g, and was maintained to 179 mAh/g even if thenumber of cycle was above 69.

The cycle life of the batteries of Example 4 and Comparative Example 4when charge-discharged at room temperature was shown in FIG. 4. As shownin FIG. 4, the initial capacity of the battery of Comparative Example 4was 170 mAh/g, but was sharply reduced along with the number of cycle tobe 97 mAh/g after 31 cycles. On the other hand, the initial capacity ofthe battery of Example 4 was 190 mAh/g, and was maintained to 166 mAh/geven if the number of cycle was above 50.

The cycle life of the batteries of Example 10 and Comparative Example 5when charge-discharged at room temperature was shown in FIG. 5. As shownin FIG. 5, the battery capacity of Example 5 and Comparative Example 10was maintained to be 92% and 83% of the initial capacity, respectively.

As can be seen from the foregoing, the electrode active material furthercomprising amphoteric compound, alkali metal sulfide or alkali metaloxide can considerably improve electrode properties.

INDUSTRIAL APPLICABILITY

As described above, lithium secondary batteries using the electrodeactive material further comprising an amphoteric compound, an alkalimetal sulfide or an alkali metal oxide neutralize acids generatingaround electrode active material so that it can inhibit the reduction inbattery capacity. In addition, the lithium secondary batteries using theelectrode active material according to the present invention areexcellent in its charge-discharge characteristics, cycle life andthermal stability.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. An electrode active material for lithium secondary batteries furthercomprising an amphoteric compound, an alkali metal sulfide or an alkalimetal oxide.
 2. The electrode active material according to claim 1,wherein the electrode is a positive electrode or a negative electrode.3. The electrode active material according to claim 2, wherein thepositive electrode active material is in the form of powder having anoxidation/reduction potential of from 1.5V to 6.0V, based on theoxidation/reduction potential of lithium metal, and is a compoundrepresented by the following formula (1):Li_(a)M_(b)N_(c)L_(d)O_(e)P_(f)Q_(g)  (1) wherein, a, b, c and d areindependently an equivalent number from 0 to 2, L, M and N areindependently selected from the group consisting of Mn, Co, Ni, Fe, Cu,Cr, Sr, Ti, V, Cu, Zn and Al, e, f and g are independently an equivalentnumber from 0 to 4, and O, P and Q are independently selected from thegroup consisting of O, S, F, Cl, Br, I, Se, Te and Fr.
 4. The electrodeactive material according to claim 2, wherein the negative electrodeactive material is in the form of powder having an oxidation/reductionpotential of from 0.001V to 3.5V, based on the oxidation/reductionpotential of lithium metal, and is graphite consisting of carbon or acompound represented by the following formulae (2) to (4):A_(x)B_(y)M_(a)N_(b)  (2) wherein x, y, a and b are independently anequivalent number from 0 to 4, A and B are independently selected fromthe group consisting of Mn, Co, Ni, Fe, Cu, Cr, Sr, Ti, V, Cu and Zn,and M and N are independently selected from the group consisting of O,S, F, Cl, Br, I, Se, Te and Fr.Si_(x)M_(y)  (3) wherein x and y are independently an equivalent numberfrom 0 to 2, and M is one element selected from the group consisting ofMn, Co, Ni, Fe, Cu, Cr, Sr, Ti, V, Cu, Zn, Al and B.SnO_(x)M_(y)  (4) wherein x and y are independently an equivalent numberfrom 0 to 4, and M is one element selected from the group consisting ofO, S, F, Cl, Br, I, Se, Te and Fr.
 5. The electrode active materialaccording to claim 1, wherein the amphoteric compound is a compoundincluding zinc, tin, lead, boron, antimony or arsenium and selected fromthe group consisting of zinc acetate, zinc acetylacetonate, zincbromide, zinc carbonate, zinc chloride, zinc iodide, zinc nitrate, zincoxide, tin acetate(II), tin acetate(IV), tin oxalate(II), tin oxide(H),tin chloride(II), lead acetate(I), lead acetate(IV), lead carbonate(II),lead chloride(II), lead nitrate(II), lead oxide(II), boron oxide, boronphosphate, boron bromide, boron chloride, boron trifluoride diethyletherate (C₂H₅)₂OBF₃), antimony oxide(III), antimony trichloride(III),antimony pentachloride(V), arsenium oxide(III), arseniumtrichloride(III) and arsenium pentachloride(V).
 6. The electrode activematerial according to claim 1, wherein the amphoteric compound isincluded in an amount of from 0.01% to 5% by weight, based on the weightof the electrode active material.
 7. The electrode active materialaccording to claim 6, wherein the amphoteric compound is included in anamount of from 0.1% to 2% by weight, based on the weight of theelectrode active material.
 8. The electrode active material according toclaim 1, wherein the alkali metal sulfide is selected from the groupconsisting of Li₂S, NaS, K₂S, Rb₂S and Cs₂S.
 9. The electrode activematerial according to claim 1, wherein the alkali metal oxide isselected from the group consisting of Li₂O, Na₂O, K₂O, Rb₂O and CS₂O.10. A method for preparing an electrode active material for lithiumsecondary batteries, comprising the steps of: adding a positiveelectrode or a negative electrode active material to a solution ofcompound selected from the group consisting of amphoteric compounds,alkali metal oxides and alkali metal sulfides in a solvent;homogeneously dispersing the mixture; and filtrating and drying thedispersed mixture to remove the solvent.
 11. The method according toclaim 10, wherein the electrode is a positive electrode or a negativeelectrode.
 12. The method according to claim 10, wherein thesolvent-removed powder is heat-treated at a temperature of from 1001 to500° C. for 1˜10 hours to coat onto the electrode active material. 13.The method according to claim 10 or 12, wherein the solvent is alcoholor water.
 14. The method according to claim 10, wherein the amphotericcompound is included in an amount of from 0.01% to 5% by weight, basedon the weight of the electrode active material.
 15. The method accordingto claim 14, wherein the amphoteric compound is included in an amount offrom 0.1% to 2% by weight, based on the weight of the electrode activematerial.
 16. The method according to claim 10, wherein the compoundselected from the group consisting of amphoteric compounds, alkali metaloxides and alkali metal sulfides is mixed in an amount of from 0.1% to20% by weight, based on the weight of the used solvent.
 17. A lithiumsecondary battery manufactured by homogeneously applying a mixture ofthe electrode active material according to claim 1, a binder and anelectrically conductive agent onto an aluminum foil or copper foil,drying to prepare a electrode, and fabricating using a separator, anelectrolyte and a packaging material.
 18. The lithium secondary batteryaccording to claim 17, wherein the electrolyte is a solution of at leastone lithium salt selected from the group consisting of LiCF₃SO₃,Li(CF₃SO₂)₂, LiPF₆, LiBF₄, LiClO₄ and LiN(SO₂C₂F₅)₂ in a solventselected from the group consisting of ethylene carbonate, propylenecarbonate, dimethyl carbonate, diethyl carbonate, methylethyl carbonate,vinylidene carbonate and γ-butyrolactone, etc., or a mixed solventthereof.
 19. The lithium secondary battery according to claim 17,wherein the separator is porous polyolefin-based polymer.
 20. Thelithium secondary battery according to claim 17, wherein the packagingmaterial is a metal can made of iron or aluminum, or a multilayered ofaluminum foil and polymer film.